trailing friction during recess, some clock makers cut away the
flanks of the driving wheel and the points of the driven wheel.
A much larger number of teeth are then, however, necessary to
secure smooth action.
< . i
Pp. 594. and 620. The Dryness of Steam.—The pro-
portionate dryness of steam at all points of the stroke can be
very conveniently represented upon the indicator diagram by
means of a simple construction. Imagine the indicator cards in
Fig. 755 to have' been obtained in the usual manner, and then to
have been plotted by the method shewn on p. 622, the clearance
volumes being of course known in terms of the cylinder volumes.
Let it also be supposed that the weight of steam passing through
the cylinders at every stroke has been found experimentally by
measuring the feed water entering the boiler, the latter being of
course only occupied in supplying stearn to the engine. Referring
a. 755. •
next to the diagram on p. 598 or to the table of saturated steam
volumes in this appendix, • the volume of i Ib. weight at 70 Ibs.
absolute pressure is found to be 6*1 cub. ft, from which the
volume of steam due to the feed water weight can be at once
deduced. Similarly the same quantity of steam, when expanded
to 30 Ibs. absolute pressure, will have a volume that may be
ascertained from the tables, or can be found by constructing the
Referring again to the diagram* the compression curves are to
fee continued, as at A.B and CD. Then at B E set off true steam